Fuel and afterburner pump system



Dec. 5, 1961 J. A. woTRING FUEL AND AFTERBURNER PUMP SYSTEM Filed Jan. 4, 1956 MSSXKR m.

United States Patent C) 3,011,308 FUEL AND AFTERBURNER PUMP SYSTE .lohn A. Wetring, Painesville, Ohio, assigner to Thompson Ramo-Wooldridge, Inc., a corporation of Ohio Filed Jan. 4, 1956, Ser. No. 557,389 1 Claim. (Cl. ell-35.6)

This invention relates generally to aircraft fuel pumping systems and more particularly relates to a fuel system for a propulsion means in an aircraft wherein all bypass fuel is returned to a point of highest pressure ahead of a fuel pump discharge and preferably at a point interstage of a multiple fuel pump including a rst centrifugal impeller stage and a subsequent positive displacement gear stage in series relationship therewith, the positive displacement gear stage including a triple element pump unit wherein the iirst element operates as a main burner pump, the second element operates as a stand-by pump unit and the third element operates as an afterburner pump unit and each of the three pump units is driven by a common driving means having a clutch to selectively inactivate the third pumping unit supplying the afterburner whenever the system demand is sufficiently diminished.

A major problem in the development of a fuel System for a jet propelled aircraft is the problem of fuel temperature rise. This problem is acute due to the large variance between fuel consumption at sea level operation and fuel consumption at high altitude operation of the jet propulsion engines.

In one form of jet aircraft engine fuel system, a con- 9 stant displacement fuel pump is provided in conjunction with a flow control unit which can be regulated in accordance with engine requirements. With such an arrangement, the fuel flow in excess of engine requirement is by-passed by the control and is returned to some point in the fuel system ahead of the control. This bypassed flow becomes a sizable percentage of pump capacity at altitudes where engine fuel consumption is low. Under such conditions, a large part of the input horsepower required to drive the fuel pump and to force pressurized fuel to the burner units of the jet engine is absorbed into the fuel system as heat. Consequently, the fuel within the fuel system is subjected to a temperature rise which may reach a point resulting in serious pumping problems.

The problem of fuel temperature rise becomes even more acute when attempts are made to satisfy the power requirements of jet propulsion power means utilizing not only a main burner but-also an afterburner. With such an arrangement, a main fuel pump is usually provided to supply fuel to the main burner units and separate pumping means are used to supply fuel to the afterburner units. Since the afterburner units are customarily used only when extra power requirements are placed upon the aircraft, the added pumping means for supplying fuel to the afterburner represent increased horsepower input to the fuel in the fuel system and also represent additional weight and space factors in the aircraft.

In the exemplary form of the present invention, a combination pump having multiple stages including a centrifugal inlet stage and a positive-displacement stage is provided. The positive-displacement stage of the cornbination pump has three separate pumping units, two of the pumping units being especially provided to supply fuel to the afterburner unit and one of the pumping units supplying fuel to the main burner. One of the pumping units normally discharging to the main burner unit constitutes a supplemental pump, the discharge of which being under the control of a transfer device operative to parallel selectively the discharge of the pump with the discharge of either the main fuel pump or the afterburner fuel pump.

1n accordance with the principles of the present inven- Cil 3,611,308 Patented Dec. 5, 1961 ICC tion, the overall performance of the triple element positive-displacement stage is enhanced by selectively inactivating the afterburner pump unit and recirculating the discharge of the stand-by pump unit so that the stand-by pump unit is always available to fill in in the event of failure or jamming of the main burner pump unit. Moreover, the stand-by pump unit produces a source of reference pressure which can be advantageously exploited to place the actuation of the afterburner pump unit on a system demand basis. In other words, the afterburner 'pump unit is maintained in idle condition except when the stand-by pump discharge is at some increment above the normal recirculation pressure so that the actuation of the afterburner pump is a function of the system demand.

By virtue of such arrangement, the fuel system by-pass pressure is materially reduced and the by-pass flow is also materially reduced. Moreover, when operating at high by-pass conditions, for the same system flow, the percentage of by-pass volume is reduced. Consequently, the normal input horsepower to the pump is less and all of the foregoing factors substantially reduce temperature rise throughout the entire fuel system.

It is an object of the present invention, therefore, to provide a fuel system for a jet engined aircraft utilizing fewer system lines and employing simplified components of less weight and occupying less space than heretofore provided.

Another object of the present invention is to provide a pump and a fuel system for an aircraft which will reduce fuel temperature rise.

Another object of the present invention is to provide a fuel system in which by-pass .flow and by-pass pressure are materially reduced.

Many other features, advantages and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheet of drawings in which a preferred structural embodiment of a fuel system incorporating the principles of the present invention is shown by way of illustrative example.

V=On the drawings:

The single drawing is a somewhat diagrammatic plumbing diagram illustrating the paths of iluid flow in connection with a pumping assembly provided in accordance with the principles of the present invention and indicating diagrammatically the control devices by means of which the present invention may be practiced.

As shown on the drawing:

The pumping assembly of the present linvention comprises a plurality of pumping units which are series-staged and it is, therefore, conceivable that completely separate pumps might be employed in order to practice the principles of the present invention. It is contemplated, however, that the entire pumping assembly illustrated in the drawing could constitute a single package pump` of a multiple unit type similar to that disclosedv in the pending application of lohn F. Murray, Serial No. 509,313, filed May 18, 1955, now Patent No. 2,972,952, assigned to the same assignee as the present application and in regard to which the present invent-ion is an improvement.

Referring to the drawing, there is indicated at 10 a fuel cell from which fluid is supplied to the inlet 11 of the pumping assembly, initial pressurization of the fluid being effected by a centrifugal pump unit indicated` diagrammatically at 121. The centrifugal pumping unit 12 discharges through a strainer 13` to a common inlet supplyring a positive displacement stage consisting of a triple element rarrangement which, in this exemplary form of the invention, includes a main burner pumpunit 14, a No. 2 or stand-by pump unit 416, and an afterburner pump unit y17.

The main burner pump unit discharges to a main burner control unit 18 and the fuel is supplied to the main burner 19 of an aircraft propulsion engine utilizing jet burners. A by-pass 20 from the main burner control 18 takes excess fuel not required at the burners 19y to a point interstage of the pump, namely, a point between the centrifugal pump unit 1% and the lpositive displacement pumping units 14, 16 and 17.

Fluid from the afterburner pumping unit 17 is supplied to an afterburner control unit 21 which controls the supply of fuel to the burners 22 of the afterburner portion of the jet engine. A by-pass 23- carries excess fuel not required by the afterburner 212 from the afterburner control 2|1 to a point interstage of the pump, namely, a point intermediate the centrifugal pumping unit 12 and the positive-displacement pumping units 14, 16 and 17.

The No. 2 or stand-by pumping unit 16 discharges to a flow-transferring means indicated generally by the reference numeral 2,4, the flow-transferring means operable to selectively parallel the discharge of the pump 16 with the discharge of the pumps 14 and 17, respectively.

The No. 2 or stand-by pumping unit 16, on starting, discharges through a flow transferring means indicated generally by the reference numeral 24 -to parallel the main burner pump unit 14, however, when a predetermined pressure is attained, the flow transferring means operates to parallel the discharge of the pump 16 with the discharge of the afterburner pump unit 17, as is described in detail in the copending application of John F. Murray, Serial No. 509,313, filed May 18, 1955.

The flow-transferring means 24 may be automatically operated by a pressure control and a suitable pressure control device is indicated diagrammatically at 26 connected to the flow-transferring means 214 by means of a linkage 27. The pressure-responsive device 26 is referenced as at 218` to discharge pressure from the main burner fuel pump 14 and is also referenced as at 29 to interstage pressure coresponding to the pressure on the inlet side of the positive-displacement pumps 14, 16 and 17.

It will be understood that Various relief valves and check valves may be supplied throughout the system for the purpose of developing the functions customarily attributed to such devices and, accordingly, further detailed description in connection with such components does not appear to be necessary to a proper understanding of the principles of the present invention.

It will be understood that the pump 16 operates as a stand-by main burner fuel pump, thereby affording a safety feature since delivery of fluid to separated points of utilization is insured. For example, if -the pump is in full operation and the pump units 16 and 17 are in parallel discharging to the afterburner control Z1 and the pump 14 is discharging to the main burner control 18, then failure of the pump 14 because of binding or seizure or some other cause of reduction in discharge pressure will reduce the pressure acting on the pressure control device 2.6 whereupon the discharge of the pump 16 will be directed to the point of utilization previously served by the pump 14.

It is desirable, therefore, that the pump unit 16 be operative at all times since it is, in effect, the emergency main burner fuel pump. There is indicated in the drawing a line 30 which carries the discharge of the stand-by pump 16 at discharge pressure and, accordingly, furnishes an excellent source of reference pressure which can be utilized as la control reference in accordance with the principles of the present invention for regulating and controlling the operation of the afterburner pump unit 17.

Thus, :the afterburner pump unit 17 is provided with a drive means common to each of the pump units 12, 14, 16 and 17, however, such driving means includes a clutch 311- which may be actuated to selectively activate or inactivate the afterburner pump unit 17.

In accordance with the principles o-f the present invention, the clutch 311 is either manually or automatically controlled and, specifically, the clutch 3:1 is provided with a pressure device responsive to the pressure control variable using the discharge pressure of the pump 16 as a source of reference pressure, thereby making actuation of the clutch 31 and activation of the afterburner pump unit 17 a pure function of the fuel system demand.

The clutch 31 is controlled by a pressure device 33 referenced to pressure in the line 30 as at 314.

A mechanical linkage is also indicated at 36 connected to a valve 37 in the line 30 to insure that the discharge of the stand-by pump unit 16 Will be utilized by the afterburner control Z1 concurrently with the activation of the afterburner pump unit 17.

llt will be understood that the pressure control 33 could be associated with the clutch 31 by means of other forms of actuating mechanisms and, for that matter, the clutch 31 could be actuated manually or electrically without the use of the pressure control 33. Accordingly, there is shown in the drawing an electric motor such as a solenoid 38 operatively connected for actuation of the clutch 31. The energization of the electric motor or solenoid 38 is controlled by a switch 39. The switch 39 is indicated as being connected to a linkage 49 operated by a manual control 4l. By virtue of such arrangement, pilot selection is available although fully automatic operation is provided. l

ln operatiomthe entire positive-displacement stage including, `for example, three separate gear pump units exemplified by the pumps 14, 16 and 17 is operated in series-staged relation with the centrifugal pumping unit 12, thereby to supply fuel to the main burner control unit 18 and the after burner control unit 21, As the aircraft rises to a higher altitude, the fuel requirements are reduced and, accordingly, since air pressure reduces as altitude increases the pressure control device 33 constitutes an altitude-responsive control to actuate at a selected value of pressure thereby to automatically clutch out the afterburner pump unit 17 upon attainment of a predetermined altitude. Concurrently therewith, the No. 2 pump unit or stand-by pump remains available for emergency use as a main fuel pump unit, however, the discharge of the stand-by unit is recirculated through the by-pass 23, 2f).

lf afterburning were required, the afterburner pump unit 17 would be automatically activated since the afterburner pump 17 would be idle except when the No. 2 pump discharge pressure was some increment above normal recirculating pressure, for example, some predetermined value of pressure such as would occur when the afterburner would be in operation. The availability of a manual override insures the possibility of pilot selection should an emergency condition arise.

Although various minor modifications might be suggested by those versed in the art, it should be understood that I Wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.

l claim as my invention:

An aircraft -fuel system comprising, a single package two-stage fuel pump having a casing formed with an inlet and an outlet and including in said casing an initial centrifugal stage in series with a positive displacement stage, two fluid discharge conduits for said pump, each carrying fuel discharged from said pump to a point of utilization, burner means for the aircraft including a main burner and an afterburner connected to said fluid connections, a main burner control, an afterburner control, both of said main burner and afterburner controls being in said fluid discharge conduits for regulating the flow of fuel to said main burner and to said afterburner, respectively, rst and second bypass conduit means bypassing fuel `from both of the main burner and afterburner controls to a point in said casing inter-stage between said centrifugal stage and said positive displacement stage, `said positive displacement stage comprising a triple element rotary intermeshing gear fluid displacement means includ- A of gears ybeing in parallel with one another, the output` of said main burner pump being discharged to said main burnerr fuel discharge conduit and the output of said afterburner pump being discharged to the afterburner discharge conduit, means for selectively leading the standby pump discharge to the main discharge conduit or the -afterbumer discharge conduit, upstream of the respective controls in said conduits, to selectively parallel the standby pump with said main pump or afterburner pump, a third bypass means =for carrying the discharge of said stand-by pump to said casing at said interstage point when the standby pump is paralleled with the afterburner pump at a recirculating pressure determined by the setting of the afterburner control unit, a common drive means for said centrifugal stage and said positive displacement stage including clutching means having an input shaft rotatably driven by said common drive means and an output shaft connected to said afterburner pump, and automatic actuating means controlling said clutching means and said second bypass means to activate said rotary intermeshing gear iluid vdisplacement means of said afterburner pump, said actuating means comprising a pressure-responl sive control device responsive to variations in said recirculating pressure for regulating said clutching and said bypass means automatically whereby the afterburner pump is activated in response to a predetermined increase in recirculating pressure due to operation of the afterburner control.

References Cited in the le of this patent UNITED STATES PATENTS 2,440,371 Holley Apr. 27, 1948 2,506,611 Neal et al May 9, 1950 2,599,680 Weeks June 10, 1952 2,617,361 Neal Nov. 11, 1952 2,633,704 Sarto Apr. 7, 1953 2,644,300 Waterman et al n July 7, 1953 2,675,828 Booth Apr. 20, 1954 2,726,507 Baker et al Dec. 13, 1955 2,774,215 Mock et al. Dec. 18, 1956 2,781,727 Marshall et al Feb. 19, 1957 2,823,518 Murray Feb. 18, 1958 FOREIGN PATENTS Great Britain I une 9, 1954 

